Multiple delete in one .sql file

Question

Hi im trying to run more than 1 delete in a single sql file (which i plan to import into a oracle database). Im very new to Oracle and im not sure how to structure it but here is my code:
DELETE FROM RESPONSEERRORS
WHERE ID IN ( SELECT EVENTRESPONSEID
FROM EVENTS
WHERE GENERATEDAT < ADD_MONTHS(SYSDATE,-1)
DELETE FROM EVENTRESPONSES
WHERE ID IN ( SELECT EVENTRESPONSEID
FROM EVENTS
WHERE GENERATEDAT < ADD_MONTHS(SYSDATE,-1)
DELETE FROM EVENTS
WHERE GENERATEDAT < ADD_MONTHS(SYSDATE,-1)
Thanks for any reply

Answer 1

Hi,
You've got the basic idea for using multiples DELETEs.
If you start that ar 11:52:14 on February 15, and each DELETE takes 2 or 3 seconds, then responseerrors might bet cut off at
11:52:15 on January 15, eventresponses might get cut off at
11:52:17, and events at
11:52:19. If anything happened to be dated in responseerrors during those 4 seconds on January 15 (or in eventresponses during those 2 seconds), then those rows will be left pointing to rows in events that no longer exist.
To avoid that, you might want to use TUNC (SYSDATE) instead of SYSDATE; that will make the cutoff time 00:00:00 on January 15 if you run the script at any time on February 15. Just be careful that you don't start it a few seconds before midnight.
If you make foreign key constraints in the "child" tables (responseerrors and eventresponses), referencing events.eventresponseid ON DELETE CASCADE, then you could simply DELETE the rows from events, and the rows in the other tables would be automaticaaly deleted, too. For details, look up foreign key constraints in the SQL Language manual:
http://download.oracle.com/docs/cd/B28359_01/server.111/b28286/clauses002.htm#sthref3021